This invention relates generally to multi-fiber optical paths and, in particular, to the use of a relatively low temperature consolidation process capable of embedding multiple fibers into a suitable material to produce optical interconnects and other useful products.
The expanding use of optical fiber cabling for data, voice and video transmission is creating a need for more efficient means for connecting optical cables of all types to each other, as well as to optical switches, devices, routers, and other devices. Most existing termination and connection methods require large numbers of small mechanical connectors applied to the fibers. Since optical networks are comprised of hundreds or thousands of fibers, these interconnection methods are slow and labor intensive.
It would be advantageous, therefore, to devise a technique whereby multiple, aligned fibers may be embedded into a material on an automated basis to provide optical cable connectors, interconnections, and so forth. Although there have been attempts to locate optical fibers into non-optical substrates, the processes used are less than optimal. For example, U.S. Pat. Nos. 4,950,043 and 5,026,140 to Russom describes a means of embedding optical fibers in titanium. The optical fibers are coated with aluminum using a process such as PVD, and then placed in a bed of titanium or titanium and aluminum powders and hot isostatically pressed to produce a solid article, with the optical fibers coated in TiAl. High temperatures and pressures are used to produce consolidation of the titanium around fibers. Such xe2x80x9cHIPingxe2x80x9d requires that batches of material be processed in a chamber, increasing cost, and making it difficult to produce very long embedded fibers, such as would be useful in a cable.
In U.S. Pat. No. 5,283,852, Gibler et al. describe a technique for embedding an optical fiber in a liquid metal by supplying special tubes to relieve stresses at the terminations of the metal-fiber zone. The inventors emphasize that allowing the fiber to exit the metal without damage would represent a significant improvement.
U.S. Pat. No. 5,245,180 to Sirkis discusses a means of interpreting data supplied by a metal coated fiber. However, the object of the invention is not to provide a more efficient means of coating fibers, or embedding them in a metal object. Sirkis suggests electroless deposition methods, vapor deposition, etc., as means of applying the needed coating.
In U.S. Pat. No. 5,289,967, Bampton et al. disclose a means of embedding optical or structural reinforcing fibers in a metal matrix. They embed the fibers in a powder and employ a transient liquid phase to produce rapid, isothermal solidification of the matrix material, preventing thermal shock and like problems associated with embedding ceramic fibers in liquid metals. Clearly, an all-solid-state process would be an improvement over this system, since transient liquid phase bonding requires careful composition control in the powders, and is very limited with respect to the materials and compositions which are suitable.
In U.S. Pat. No. 6,012,856, Kim et al. describes a means of reinforcing a splice between metal coated optical fibers. The metal coated fibers are spliced together, but the joint is not strong enough to allow bending of the fibers during installation. According to the process, a second connector is added with a grooved for locating the fibers, to which an adhesive is added. In U.S. Pat. No. 6,193,421, Tamekuni et al. describe a means of fixturing a previously metal coated fiber in a groove, without exerting pressure on it, so that a fiber can be placed. U.S. Pat. No. 6,219,484 to Rhee et al. describes a means of placing previously metal coated fibers, terminating them and bonding them to another previously metal coated layer via laser soldering or an epoxy filling. U.S. Pat. No. 6,303,182 Eggleton, et al. describes the coating of an optical fiber with a thin coating for the purpose of locally affecting mechanical or physical properties of the fiber. Evaporative coatings are cited as a means of deposition, while a mask is used to ensure local deposition or lack thereof.
Not only would multiple aligned fibers provide a foundation for optical cable connectors and interconnections, if an electrical conductor were used as the surrounding material the fibers could be used for reinforcement or, more optimally, to create a combination signal and power-carrying cable combination. Electrical transmission lines are typically fabricated from copper for its high conductivity. High purity aluminum has very high conductivity also, and is much lighter and cheaper than copper, making it an attractive material for electrical transmission lines. However, the low strength and creep resistance of high purity aluminum cause problems in practical application.
Fiber reinforcement has been suggested as a means of rendering high purity aluminum sufficiently strong and creep resistant to function as an electrical transmission line material. U.S. Pat. Nos. 6,180,232 and 6,245,425 to McCullough et al. have claimed a means of producing a fiber reinforced transmission line which makes use of polycrystalline alumina (Al2O3) fibers to reinforce a substantially pure aluminum alloy or an alloy containing up to 2% copper, as a transmission line material with enhanced properties. In order to form this material, McCullough discloses a method much like that provided in U.S. Pat. No. 5,002,836 to Dinwoodie et al. to produce metal matrix composites and articles fabricated therefrom.
However, the methods proposed by McCullough, Dinwoodie, and others, rely on infiltration of fiber bundles with molten aluminum. Much of the art disclosed deals with means of addressing the numerous problems created when a ceramic fiber is exposed to molten aluminum, such as thermal shock, the tendency of the fiber to dissolve, and the production of undesirable second phase particles at the fiber-matrix interface which detract from the interface bond quality.
Thus, despite these advances, the need nevertheless remains for a technique capable of rapidly and precisely locating and fixturing large numbers of optical fibers. Such an approach would provide benefits in reducing the cost of optical systems, and decreasing loss at interconnections. Advantageously, should the material used to embed the fibers itself be electrically conductive, the possibility exits for an integrated signal-and power-carrying cable.
This invention improves upon prior art methods and apparatus by providing a continuous, single-step, low-temperature process to embed one or more optical fibers into a surrounding material. In contrast to existing approaches, the process combines metal coating with splicing of fibers, producing a single, continuous low-cost process for embedding fibers in a metal, alloy, or other suitable material, as well as splicing fibers with a joint of uniform composition requiring no additional adhesives, resulting in high strength. A range of metals are suited to this process, including aluminum, copper, titanium, nickel, iron, and alloys thereof, as well a numerous other of materials of perhaps more limited structural utility.
Broadly, the invention provides a method of depositing and consolidating material without the need for a binder. The technique affords many of the advantages of 3-D printing, including small particle size and material flexibility. It is well suited to the embedding of optical fibers because the process uses small feedstock particles which minimize the pressure applied around the fibers to consolidate them, thereby reducing the chance of fiber damage. The method can be used to create terminations for cables, or it can be used as a method of splicing or joining optical fibers by positioning the ends of the two fibers under the foils, so that they abut prior to creating the bond. The consolidation material may be provided in sheets, with or without fiber-locating grooves or, alternatively, droplets may be used. In the preferred embodiment, ultrasonic vibrations are used as the source of consolidation energy.
In the preferred embodiment the embedded fibers carry low-power optical signals as a means of data transmission. In alternative embodiments, however, the fiber(s) function as a sensor, or as a reinforcement, since quartz fibers are themselves quite strong, the invention may be used in other applications, including. For example, with respect to electrical power transmission, a high-purity, high-conductivity aluminum wire with continuous structural fiber reinforcement according to the invention may be employed to make it strong and creep resistant. Moreover, if the fiber(s) carry data transmissions, such a reinforcing effect may achieved along with sufficient bandwidth to supply commercial and residential businesses. Optionally, a combination of structural and optical fibers could be used for reinforcement purposes. If one or more of the fibers are employed as a sensor, a cable with integrated breakage detection may be realized.